Desulfurization Agent Containing Bitumen, Method for the Production Thereof, and Use Thereof

ABSTRACT

An agent for desulfurizing and/or for pre-desulfurizing, in particular for desulfurizing and/or pre-desulfurizing molten pig iron or molten steel, contains calcium oxide and bitumen.

The present invention relates to an agent for desulfurizing and/orpre-desulfurizing, in particular for desulfurizing and/orpre-desulfurizing molten pig iron or molten steel, to a method ofmanufacturing such an agent and to the use of such an agent fordesulfurizing and/or pre-desulfurizing molten pig iron or molten steel.

A mixture of iron ore and coke which acts both as an energy carrier andas a reductant for the iron ore is typically reduced to pig iron in afurnace for manufacturing pig iron. Due to the comparatively high sulfurcontent of coke, comparatively high sulfur quantities are introducedinto the molten pig iron in this method. Since a high sulfur contentnegatively impairs the mechanical properties both of cast ironmanufactured from the pig iron and of steel manufactured from the pigiron, the sulfur introduced in the pig iron extraction has to be removedfrom the pig again and/or from the steel manufactured therefrom again toset the desired sulfur content.

A plurality of desulfurization agents have been proposed to removesulfur from pig iron and/or from steel which are, for example,introduced pneumatically or mechanically into the molten pig iron ormolten steel and reduce the sulfur there to a sulfur compound such ascalcium sulfide which rises in the molten pig iron and thus passes intothe slag with which it is later removed from the pig iron. Magnesium,magnesium alloys, soda, burnt lime, and calcium carbide are, forexample, known as reductants for desulfurization. It is additionallyknown to add a further compound to such reductants to increase theirefficiency in the desulfurizing of pig iron and/or steel. Adesulfurizing agent is thus disclosed in DE 22 52 796 C3 which containsa solid compound containing hydrogen such as polyethylene or polyamideas a reductant in addition to calcium chloride or calcium cyanamide.Furthermore, a desulfurization agent is known from EP 0 226 994 B1 whichcontains calcium carbide and dried coal.

A number of the above-named desulfurization agents, however, haveproperties disadvantageous for pig iron desulfurization. For example,soda decomposes explosively on the introduction into the pig iron, whichresults in increased wear of the involved components. In addition, thedegrees of desulfurization which can be achieved with soda areunsatisfactorily low. Furthermore, soda reacts exothermally with sulfurso that temperature losses occur in the pig iron. The degrees ofdesulfurization achievable with magnesium and magnesium alloys as thedesulfurization agent are also limited, and indeed inter glia due to thefact that the solubility of magnesium increases as the temperature ofthe pig iron increases and the sulfur content drops. The above-namedcalcium compounds such as polyethylene, polyamide and dried coal, addedto calcium carbide to increase the degree of desulfurization also havedisadvantages. The addition of plastics such as polyethylene orpolyamide to the calcium carbide degrades the injection behavior of thedesulfurization agent into the molten pig iron. Furthermore dried coalsare prone to self-ignition in air. In addition, they have to be admixedwith the calcium carbide—due to the high reactivity of calcium carbidewith water—with a sufficiently low moisture content so that such coalsare expensive and require an increased effort with respect to storageand transport.

For this reason, primarily desulfurization agents based on calciumcompounds such as calcium carbide, calcium oxide, calcium hydroxide orcalcium carbonate are used for desulfurizing molten pig iron and/ormolten steel. Of these, calcium carbide has the highest specificefficiency in desulfurization, i.e. a desulfurization of molten pig ironhigher by approximately a factor of 2 is achieved with a predefinedquantity of calcium oxide than with the same quantity of calcium oxide.Calcium carbide reacts with water while forming acetylene which, likeall low molecular hydrocarbons forms easily flammable mixtures with air.For this reason, the transport and the storage of calcium carbide arecomplex and cost-intensive. Against this background, an agent fordesulfurizing molten pig iron or molten steel based on calcium oxidewith a high desulfurization efficiency would be desirable.

It is therefore the object of the present invention to provide adesulfurization agent based on calcium oxide which has a high specificefficiency in the desulfurizing of molten pig iron or molten steel.

This object is satisfied in accordance with the invention by an agentfor desulfurizing and/or pre-desulfurizing, in particular fordesulfurizing or pre-desulfurizing molten pig iron or molten steel,which contains calcium oxide and bitumen.

This solution is based on the surprising recognition that the admixtureof bitumen to calcium oxide significantly reduces the efficiency ofcalcium oxide in the desulfurization and/or pre-desulfurization ofmolten. pig iron or molten steel—in comparison with the same mixturewithout a bitumen admixture—and indeed in dependence on the respectivedifferent works-specific physical, chemical and technological conditionsup to the desulfurization power of calcium carbide. In this respect, itis of particular advantage that the admixed bitumen does not impair, orat least does not significantly impair, the injection behavior of thedesulfurization agent into the molten pig iron. Apart from this, bitumenis stable in air, is not auto-ignitable and is not reactive with waterso that bitumen is not subject to any transport restrictions or storagerestrictions. Overall, the desulfurization agent thus has the advantagesof calcium oxide while simultaneously avoiding the disadvantages of thedesulfurization agent known from the prior art.

Bitumen is a mixture of high molecular weight hydrocarbons which bothoccurs naturally and can also be manufactured, for example, by vacuumdistillation from crude oil. In this respect, bitumen is the crude oilfraction with the highest boiling point and the non-boiling crude oilfraction which are not modified in vacuum distillation. Bitumen is adispersion in which high-carbon particles, the so-called asphaltenes, aswell as resins in an oily base mass, whose components are calledmaltenes, are present in colloidally dissolved form. The maltenes areprimarily aromatic hydrocarbons, cycloalkanes, alkanes and alkeneshaving a molecular weight meaned over the weight of 500 to 1,500 g/molin each case, whereas the asphaltenes comprise aromatic hydrocarbons andheterocyclic compounds having a comparatively high molecular weight.

Bitumen is understood in the sense of the present invention as all ofthe corresponding compositions defined in DIN EN 12597, that is inparticular also asphalts—all mixtures of bitumen and aggregates—as wellas all fractions which have been obtained from bitumen and/or asphalt byany desired separation technique.

Within the framework of the present invention, all naturally occurringbitumens and all bitumen manufactured synthetically, for example fromcrude oil, can be used as the bitumen, and indeed independently ofwhether they are present in solid form, paste-like form or liquid form.Those can be named in this connection, for example, which are selectedfrom the group which consists of road construction bitumen, hard roadconstruction bitumen, soft bitumen, modified bitumen, distillationbitumen, high-vacuum bitumen, polymer-modified bitumen, special bitumen,industrial bitumen, oxidation bitumen, hard bitumen, blended bitumen,cold bitumen, fluxed bitumen, flux bitumen, natural asphalt and anydesired mixtures of two or more of the aforesaid compounds, wherein theindividual terms arc in turn meant in the meaning specified in DIN EN12597.

The present invention is generally not restricted with respect to thequantity of bitumen contained in the desulfurization agent. For example,the desulfurization agent in accordance with the invention can contain0.1 to 20% by weight of bitumen. The quantity of bitumen contained inthe desulfurization agent, however, preferably amounts to 1 to 10% byweight, particularly preferably to 2 to 6% by weight, and veryparticularly preferably to 2 to 4% by weight.

As presented above, the calcium oxide contained in the desulfurizationagent in accordance with the invention acts as a reductant for thesulfur contained in the molten pig iron or molten steel. In general, inaddition to the calcium oxide, the desulfurization agent can containother reductants, in particular based on another calcium compound. Inthe last-named embodiment, the desulfurization agent contains a mixtureof two or more calcium compounds, with this mixture, which is alsocalled a calcium component, preferably containing at least 20% by weightof calcium oxide and the remainder to 100% by weight being one or morecompounds selected from the group consisting of calcium hydroxide,calcium carbonate, calcium carbide, and any desired mixtures of two ormore of the aforesaid compounds. It is preferred due to theclassification of calcium carbide as a hazardous material and to thetransport and storage restrictions accompanying it that the quantity ofcalcium carbide contained in the desulfurization agent is as low aspossible or that the desulfurization agent particularly preferably doesnot contain any calcium carbide at all, that is the desulfurizationagent contains a mixture of two or more calcium compounds, with thismixture containing at least 20% by weight of calcium oxide and theremainder to 100% by weight being calcium hydroxide and/or calciumcarbonate.

It is proposed in a further development of the idea of the inventionthat the calcium component or the mixture of calcium compounds of thedesulfurization agent in accordance with the invention comprises atleast 50% by weight of calcium oxide, preferably at least 75% by weightof calcium oxide, in particular preferably at least 90% by weight ofcalcium oxide, particularly preferably at least 95% by weight of calciumoxide, and very particularly preferably at least 99% by weight ofcalcium oxide.

In accordance with a very particularly preferred embodiment of thepresent invention, the desulfurization agent contains calcium oxide asthe only calcium compound.

A calcium oxide manufactured in all manners, such as soft burnt lime,medium burnt lime and hard burnt lime, can be used as the calcium oxide,with good results in particular being achieved with soft burnt lime.

In principle, the present invention is not restricted with respect tothe quantity of the calcium oxide in the desulfurization agent inaccordance with the invention. Good results are, however, in particularobtained when the desulfurization agent contains 80 to 99.9% by weightof calcium oxide, preferably 84 to 98% by weight of calcium oxide,particularly preferably 90 to 97% by weight of calcium oxide, and veryparticularly preferably 94 to 96% by weight of calcium oxide or amixture thereof which contains at least 20% by weight of calcium oxide,preferably at least 50% by weight of calcium oxide, in particularpreferably at least 75% by weight of calcium oxide, particularlypreferably at least 90% by weight of calcium oxide, particularlypreferably at least 95% by weight of calcium oxide, and most preferablyat least 99% by weight of calcium oxide and the remainder to 100% beingone or more compounds selected from the group consisting of calciumhydroxide, calcium carbonate, calcium carbide and any desired mixturesof two or more of the aforesaid compounds.

In accordance with an embodiment of the present invention, thedesulfurization agent, in particular when it is designed forcoinjection, preferably does not contain any other compoundconventionally used for the reduction of sulfur such as in particular nomagnesium, no magnesium alloy and no soda.

Provided that the desulfurization agent is to be introduced into thesmelt to be treated by monoinfection, it can, however, in an alternativeembodiment contain magnesium and/or a magnesium alloy such as inparticular a magnesium aluminum alloy. It is preferred in thisembodiment that the desulfurization agent contains 1 to 15% by weight,and preferably 6 to 12% by weight, of magnesium and/or of a magnesiumalloy, preferably of a magnesium aluminum alloy.

Good results are in particular obtained in the above embodiment when themagnesium and/or magnesium alloy, preferably a magnesium aluminum alloy,contained in the desulfurization agent is particulate and when at least99% of all particles have a diameter of at least 30 μm, preferably of 30to 200 μm, and particularly preferably of 50 to 200 μm. Thedesulfurization agent in this embodiment consequently particularlypreferably contains 1 to 15% by weight, and very particularly preferably6 to 12% by weight, of magnesium and/or of a magnesium alloy, having apreviously described grain size.

In addition to the bitumen and the calcium oxide, and optionallymagnesium and/or a magnesium alloy, the desulfurization agent inaccordance with the invention preferably contains a flux agent toincrease the flow behavior of the calcium oxide which has littleflowability per se. All compounds known to the skilled person for thispurpose can be used as the flux agent, with good results in particularbeing obtained with multivalent alcohols and silicone oils. Additionallyor alternatively to this, bituminous coals can also be used as the fluxagent. Examples for suitable multivalent alcohols are in partiuclarglycols, whereas examples for particularly suitable silicone oils areorganopolysiloxanes such as in particular polymethylhydrogensiloxanes.

The desulfurization agent in accordance with the invention preferablycontains between 0.01 and 10% by weight, and particularly preferablybetween 0.05 and 5% by weight of one or more flux agents. Thedesulfurization agent in accordance with the invention in particularpreferably contains between 0.05 and 0.5% by weight, further preferablybetween 0.05 and 0.2% by weight of one or more flux agents, veryparticularly preferably between 0.075 and 0.125% by weight of one ormore flux agents, and most preferably approximately 0.1% by weight ofone or more flux agents. Provided bituminous coal is contained as theflux agent, the amount of bituminous coal preferably amounts to 4 to 8%by weight with respect to the total weight of the desulfurization agent.

Apart from the bitumen, the calcium oxide, the optional magnesium or theoptional magnesium alloy and the optional, but preferred flux agent, thedesulfurization agent in accordance with the invention can contain oneor more additives. The desulfurization agent preferably contains atleast one additive which is selected from the group which consists ofcryolite, sodium borate, fluorite and any desired mixtures of two ormore of the above compounds.

The amount of additives contained in the desulfurization agentpreferably amounts to 0.5 to 8% by weight, particularly preferably to0.5 to 4% by weight, and very particularly preferably to 0.5 to 2% byweight.

In accordance with a particularly preferred embodiment of the presentinvention, the desulfurization agent is composed of or comprises:

i) 0.1 to 20% by weight bitumen, preferably 1 to 10% by weight bitumen,particularly preferably 2 to 6% by weight bitumen, and very particularlypreferably 2 to 4% by weight bitumen;

ii) 0.01 to 10% by weight of a flux agent, preferably 0.05 to 0.5% byweight of a flux agent, particularly preferably 0.05 to 0.2% by weightof a flux agent, very particularly preferably 0.075 to 0.125% by weightof a flux agent, and most preferably approximately 0.1% by weight of aflux agent, said flux agent being selected from the group consisting ofmultivalent alcohols, bituminous coal and silicone oils and any desiredmixtures thereof, preferably being selected from the group consisting ofglycols, organopolysiloxanes, and any desired mixtures thereof, andparticularly preferably of a polymethylhydrogensiloxane;

iii) 0 to 15% by weight of magnesium and/or of a magnesium alloy,preferably of a magnesium aluminum alloy, preferably 1 to 15% by weightof magnesium and/or of a magnesium alloy, preferably of a magnesiumaluminum alloy, and particularly preferably 6 to 12% by weight ofmagnesium and/or of a magnesium alloy, preferably of a magnesiumaluminum alloy;

iv) 0 to 10% by weight of an additive, preferably 0.5 to 8% by weight ofan additive, particularly preferably 0.5 to 4% by weight of an additive,and particularly preferably 0.5 to 2% by weight of an additive, saidadditive being selected from the group consisting of cryolite, sodiumborate, fluorite, and any desired mixtures of two or more of the abovecompounds; and

v) remainder to 100% by weight being calcium oxide or a mixture whichcontains at least 20% by weight of calcium oxide, preferably at least50% by weight of calcium oxide, in particular preferably 75% by weightof calcium oxide, particularly preferably at least 90% by weight ofcalcium oxide, very particularly preferably at least 95% by weight ofcalcium oxide, and most preferably 99% by weight of calcium oxide, andthe remainder to 100% being one or more compounds selected from thegroup consisting of calcium hydroxide, calcium carbonate, calciumcarbide, and any desired mixtures of two or more of the aforesaidcompounds.

In accordance with a particularly preferred embodiment of the presentinvention, the desulfurization agent is composed of or comprises:

i) 2 to 4% by weight bitumen;

ii) 0.05 to 0.2% by weight of a flux agent selected from the groupconsisting of glycols, polymethylhydrogensiloxanes and any desiredmixtures thereof;

iii) 0 to 15% by weight of magnesium and/or of a magnesium alloy, andpreferably 6 to 12% by weight of magnesium and/or of a magnesium alloy;

iv) 0.5 to 2% by weight of an additive selected from the groupconsisting of cryolite, sodium borate, fluorite, and any desiredmixtures of two or more of the above compounds; and

v) the remainder to 100% being calcium oxide.

In accordance with a very particularly preferred embodiment of thepresent invention alternative to this, the desulfurization agentcomprises or consists of:

i) 2 to 3% by weight of bitumen;

ii) 4 to 5% by weight of a flux agent selected from the group consistingof glycols, bituminous coals and any desired mixtures thereof;

iii) 0 to 15% by weight of magnesium and/or of a magnesium alloy, andpreferably 6 to 12% by weight of magnesium and/or of a magnesium alloy;

iv) 0.5 to 2% by weight of an additive selected from the groupconsisting of cryolite, sodium borate, fluorite, and any desiredmixtures of two or more of the above compounds; and

iv) remainder to 100% being calcium oxide.

The desulfurization agent preferably has a flowability of at least 40cm, preferably of at least 45 cm, particularly preferably of at least 55cm, very particularly preferably of at least 60 cm, and most preferablyof at least 65 cm. In this respect, the flowability is determined in anair conveying channel as follows: A pneumatic conveying channel is usedwhich comprises an air box having a gas-permeable fabric, wherein thefabric has a width of 0.1 m and a length of 1.5 m and the fabric isaerated by a fan with a defined volume flow of 20 m³/h air from below. Afabric is used having a specific fabric load of 1.6 m³/(min*m²), whereinthe specific fabric load is understood as the air quantity in m³ perminute and per m² fabric area. The inclination of the conveying channelis set to 2°. A sample having a weight of 300 g is then weighed and isplaced at the upper end of the air conveying channel and the outflowlength in cm is determined, with the outflow length to be understood asthe path length of the material conveyed by the air flow. In thisrespect, the measurement takes place in the middle of the conveyingchannel. The conveying channel is then cleaned using an industrialvacuum cleaner and the procedure is repeated successively with fourfurther samples having a weight of 300 g respectively. The respectivelargest value and the respective smallest value of the values obtainedfor the outflow length are eliminated and the arithmetic mean of theremaining three values is formed. This arithmetic mean is theflowability.

In a further development of the idea of the invention, it is proposedthat the desulfurization agent in accordance with the invention ispresent in the form of a mixture, and indeed preferably in the form of ahomogeneous mixture.

In this respect, at least the calcium oxide contained in thedesulfurization agent in accordance with the invention has such adistribution of a range of grain sizes that at least 80% by weight ofthe calcium oxide has a grain size of less than 32 μm, at least 85% byweight of the calcium oxide has a grain size of less than 45 μm, atleast 90% by weight of the calcium oxide has a grain size of less than63 μm, and at least 95% by weight of the calcium oxide has a grain sizeof less than 90 μm.

All the components of the desulfurization agent, with the exception ofthe magnesium and/or of the magnesium alloy optionally containedtherein, preferably have an above distribution of a range of grainsizes, that is on in which at least 80% by weight of the components hasa grain size of less than 32 μm, at least 85% by weight of thecomponents has a grain size of less than 45 μm, at least 90% by weightof the components has a grain. size of less than 63 μm, and at least 95%by weight of the components has a grain size of less than 90 μm.

It is furthermore also possible that all the components of thedesulfurization agent have such a distribution of a range of grainsizes, i.e. that at least 80% by weight of the desulfurization agent hasa grain size of less than 32 μm, at least 85% by weight of thedesulfurization agent has a grain size of less than 45 μm, at least 90%by weight of the desulfurization agent has a grain size of less than 63μm, and at least 95% by weight of the desulfurization agent has a grainsize of less than 90 μm.

In accordance with a further particularly preferred embodiment of thepresent invention, the desulfurization agent has the form of one or morebriquettes and preferably of one or more cushion-shaped briquettes. Thebriquette or briquettes preferably has/have a size (length×width) viewedin cross-section of 10×5 to 200×100 mm, preferably of 25×15 mm to 75×50mm, and particularly preferably of 40×20 to 50×30 mm, such as of 45×25mm. Such a briquette-shaped desulfurization agent is surprisinglycharacterized by a particularly high desulfurization effect for moltenpig iron. In addition, such a briquette-shaped desulfurization agentsurprisingly considerably reduces the total oxygen content of slag sothat it is in particular also suitable for the slag treatment anddesulfurization of pig iron.

The briquette-shaped desulfurization agent preferably contains bitumen,calcium oxide, optionally a further calcium compound and optionally oneor more additives, with the above compounds preferably being selectedfrom the above-named groups and being contained in the above-describedquantities.

In accordance with a particularly preferred embodiment of the presentinvention, the briquette-shaped desulfurization agent consists ofbitumen, calcium oxide, optionally one or more further calcium compoundsand optionally one or more additives, with the above compoundspreferably being selected from the above-named groups and beingcontained in the above-described quantities, i.e. the desulfurizationagent in accordance with this embodiment does not contain any furthercomponents except for the above-named components and in particularcontains no flux agent and also no magnesium or no magnesium alloy. Thebriquette-shaped desulfurization agent in accordance with thisembodiment is in particular suitable for slag treatment.

In a further development of the idea of the invention, it is proposedthat the briquette-shaped desulfurization agent is composed of:

i) 0.1 to 20% by weight of bitumen, preferably 1 to 10% by weight ofbitumen, particularly preferably 2 to 6% by weight of bitumen, and veryparticularly preferably 2 to 4% by weight of bitumen;

ii) 0 to 10% by weight of an additive, preferably 0.5 to 8% by weight ofan additive, particularly preferably 0.5 to 4% by weight of an additiveand particularly preferably 0.5 to 2% by weight of an additive selectedfrom the group consisting of cryolite, sodium borate, fluorite, and anydesired mixtures of two or more of the above compounds; and

iii) remainder to 100% being calcium oxide or of a mixture whichcontains more than 0% by weight of calcium oxide, but at most 99% byweight of calcium oxide, preferably at most 95% by weight of calciumoxide, in particular preferably at most 90% by weight of calcium oxide,particularly preferably at most 75% by weight of calcium oxide, and veryparticularly preferably at most 50% by weight of calcium oxide and aremainder to 100% being one or more compounds selected from the groupconsisting of calcium hydroxide, calcium carbonate, calcium carbide andany desired mixtures of two or more of the aforesaid compounds.

A further subject of the present invention is a method of manufacturinga previously described agent for desulfurizing, in particular fordesulfurizing molten pig iron or molten steel, which comprises thefollowing steps:

a) mixing of i) calcium oxide; bitumen; iii) optionally, at least oneflux agent; iv) optionally, at least one further additive; as well as v)one or more calcium compounds selected from the group consisting ofcalcium hydroxide, calcium carbonate, calcium carbide and any desiredmixtures of two or more of the aforesaid compounds; and

b) grinding the mixture obtained in step a) to powder having adistribution of a range of grain sizes in which at least 80% by weightof the powder has a groin size of less than 32 μm, at least 85% byweight of the powder has a grain size of less than 45 μm; at least 90%by weight of the powder has a grain size of less than 63 μm, and atleast 95% by weight of the powder has a grain size of less than 90 μm.

The starting materials, i.e. i) calcium oxide; ii) optionally bitumen;iii) at least one flux agent; iv) optionally, at least one furtheradditive as well as v) one or more calcium compounds selected from thegroup consisting of calcium hydroxide, calcium carbonate, calciumcarbide and any desired mixtures of two or more of the above compoundshaving a grain size of in each case a maximum of 20 mm are preferablyadded and then mixed with one another in the method step a).

It is proposed in a further development of the idea of the invention togrind the mixture obtained in method step a) to powder having a grindingfineness of 90 R 5 in method step b) and preferably to powder having adistribution of a range of grain sizes in which at least 80% by weightof the powder has a grain size of less than 32 μm, at least 85% byweight of the powder has a grain size of less than 45 μm, at least 90%by weight of the powder has a grain size of less than 63 μm, and atleast 95% by weight of the powder has a grain size of less than 90 μm.

For the comminution of the mixture manufactured in method step a) inmethod step b), all apparatus familiar to the skilled person can be usedwith which corresponding mixtures can be comminuted. Non-restrictiveexamples for these are granulators, impact mills and hammer mills.

Provided that the desulfurization agent to be manufactured isadditionally intended to contain magnesium and/or a magnesium alloy, itis preferred not to admix it and/or them in method step a), but ratherto admix it and/or them to the already ground mixture after the methodstep b). The reason for this is that, as presented above, at least thecalcium oxide contained in the desulfurization agent is to be ground toa comparatively small grain size, namely to one having a distribution ofa range of grain sizes at which at least 80% by weight of the calciumoxide has a grain size of less than 32 μm. Such a small grain size is,however, not advantageous for the magnesium or the magnesium alloyoptionally contained in the desulfurization agent because this wouldproduce an explosive atmosphere on grinding. It is therefore proposed inaccordance with a preferred embodiment of the present invention only toadmix the optional magnesium and/or the optional magnesium alloy aftermethod step b), and indeed as particulate magnesium and/or particulatemagnesium alloy, with at least 99% of all particles having a diameter ofat least 30 μm, preferably of at least 30 to 200 μm and particularlypreferably from 50 to 200 μm.

A mixture is preferably manufactured by the method which consists of

i) 0.1 to 20% by weight of bitumen, preferably 1 to 10% by weight ofbitumen, particularly preferably 2 to 6% by weight of bitumen, and veryparticularly preferably 2 to 4% by weight of bitumen;

ii) 0.01 to 10% by weight of a flux agent, preferably 0.05 to 0.2% byweight of a flux agent, very particularly preferably 0.075 to 0.125% byweight of a flux agent and mostpreferably approximately 0.1% by weightof a flux agent selected from the group consisting of multivalentalcohols, bituminous coals and silicone oils and any desired mixturesthereof, preferably selected from the group consisting of glycols,organopolysiloxanes and any desired mixtures thereof and particularlypreferably of a polymethylhydrogensiloxane;

iii) 0 to 15% by weight of magnesium and/or of a magnesium alloy,preferably 1 to 15% by weight of magnesium and/or of a magnesium alloy,and particularly preferably 6 to 12% by weight of magnesium and/or of amagnesium alloy;

iv) 0 to 10% by weight of an additive, preferably 0.5 to 8% by weight ofan additive, particularly preferably of 0.5 to 4% by weight of anadditive, and particularly preferably 0.5 to 2% by weight of an additiveselected from the group consisting of cryolite, sodium borate, fluoriteand any desired mixtures of two or more of the above compounds; and

iv) the remainder to 100% being calcium oxide or of a mixture whichcontains at least 20% by weight of calcium oxide, preferably at least50% by weight of calcium oxide, in particular preferably al least 75% byweight of calcium oxide, particularly preferably at least 90% by weightof calcium oxide, very particularly preferably at least 95% by weight ofcalcium oxide, and most preferably at least 99% by weight of calciumoxide and the remainder to 100% by weight being one or more compoundsselected from the group consisting of calcium hydroxide, calciumcarbonate, calcium carbide and any desired mixtures of two or more ofthe above-named compounds.

The present invention finally relates to the use of the previouslydescribed agent for desulfurizing and/or pre-desulfurizing and/or forthe slag treatment of molten pig iron or molten steel.

The agent for desulfurization is preferably introduced into the moltenpig iron or into the molten steel by an immersion lance process using atransport gas, preferably argon or nitrogen, or by a stirring-inprocess, and indeed preferably in an amount of 2 to 5 kg per tonnemolten pig iron or molten steel.

In particular when the agent is used for pre-desulfurization and/or forthe slag treatment of molten pig iron or molten steel, it isparticularly preferred to provide the agent in the form of one or morebriquelles and to add them to the molten pig iron or molten steel.

The present invention will be further described in the following withreference to these examples, which illustrate the present invention, butwhich are, however, not restrictive.

EXAMPLE

A mixture was manufactured by mixing:

-   -   93.9% by weight of calcium oxide;    -   6% by weight hard bitumen; and    -   0.1% by weight silicone oil (flux agent).

This mixture was mixed homogeneously in a mixer and ground to a powderhaving a distribution of a range of grain sizes in which 84.30% byweight of the powder has a grain size of less than 32 μm, 87.9% byweight of the powder has a grain size of less than 45 μm, 90.1% byweight of the powder has a grain size of less than 63 μm, and at least95.12% by weight of the powder has a grain size of less than 90 μm.

The desulfurization agent thus obtained was injected into an amount of1.1 kg/t pig iron by an immersion lance process in multiinjection withrespect to the mixture involved containing lime and bitumen. In thisrespect, at pig iron temperatures around 1300° C. with unchanginginjection amounts of the other substances involved in themultiinjection, 350 ppm sulfur was removed from the molten pig iron.

Pig iron having a sulfur content of 26 ppm on average was obtained.

Comparison Example

A desulfurization agent was manufactured as described in the example,with the exception that it does not contain any bitumen.

A mixture was rathcr manufactured by mixing:

-   -   97.9% by weight technical calcium carbide;    -   2.0% by weight cryolite (additive); and    -   0.1% by weight silicone oil (flux agent).

This mixture was ground as described in the example and was introducedinto molten pig iron by an immersion lance process in multiinjectionwhile taking account of the same technological conditions at the sameplane with 1.1 kg/t pig iron.

Pig iron having a sulfur content of 25 ppm was obtained.

1-23. (canceled)
 24. An agent for desulfurizing and/or pre-desulfurizingwhich contains calcium oxide, bitumen as well as between 0.01 and 10% byweight of at least one flux agent, wherein the at least one flux agentis selected from the group of members consisting of multivalentalcohols, bituminous coal, silicone oils and mixtures thereof, andwherein the agent does not contain any calcium carbide, any magnesium orany magnesium alloy.
 25. The agent in accordance with claim 24, whereinthe bitumen is selected from the group of members consisting of roadconstruction bitumen, hard road construction bitumen, soft bitumen,modified bitumen, distillation bitumen, high-vacuum bitumen,polymer-modified bitumen, special bitumen, industrial bitumen, oxidationbitumen, hard bitumen, blended bitumen, cold bitumen, fluxed bitumen,flux bitumen, natural asphalt and any desired mixtures of two or more ofthe aforesaid compounds.
 26. The agent in accordance with claim 24containing 0.1 to 20% by weight of bitumen.
 27. The agent in accordancewith claim 24 further containing a mixture of two or more calciumcompounds which contains at least 20% by weight calcium oxide and aremainder to 100% by weight being one or more compounds selected fromthe group of members consisting of calcium hydroxide, calcium carbonate,and any desired mixtures of the aforesaid compounds.
 28. The agent inaccordance with claim 27, wherein the mixture of calcium compounds iscomposed of at least 50% by weight calcium oxide.
 29. The agent inaccordance with claim 27 containing calcium oxide as the only calciumcompound.
 30. The agent in accordance with claim 27, wherein the calciumoxide is manufactured as soft burnt lime.
 31. An agent in accordancewith claim 27, wherein the agent has a flowability of at least 40 cm,wherein the flowability is determined in an air channel in that apneumatic air channel is used which comprises an air box having agas-permeable fabric, wherein the fabric has a width of 0.1 m and alength of 1.5 m and the fabric is aerated by a fan with a defined volumeflow of 20 m³/h air from below; a fabric is used having a specificfabric load of 1.6 m³/(min*m²), wherein the specific fabric load isunderstood as the air quantity in m³ per minute and per m² fabric area;the inclination of the conveying channel is set to 2° and then a samplehaving a weight of 300 g is weighed and is placed at the upper end ofthe air conveying channel and the outflow length in cm is determined,with the outflow length to be understood as the path length of thematerial conveyed by the air flow; in this respect, the measurementtakes place in the middle of the conveying channel and the conveyingchannel is then cleaned using an industrial vacuum cleaner and theprocedure is repeated successively with four further samples having aweight of 300 g respectively; the respective largest value and therespective smallest value of the values obtained for the outflow lengthare eliminated and the arithmetic mean of the remaining three values isformed, with this arithmetic mean being the flowability.
 32. The agentin accordance with claim 24 containing 80 to 99.9% by weight of amixture of calcium compounds or 80 to 99.9% by weight of calcium oxideas the only calcium compound.
 33. The agent in accordance with claim 24,wherein the at least one flux agent is selected from the group ofmembers which consists of glycols, organopolysiloxanes, mixturesthereof, and polymethylhydrogensiloxane.
 34. The agent in accordancewith claim 24 containing between 0.05 to 5% by weight of one or moreflux agents.
 35. The agent in accordance with claim 24 furthercontaining at least one additive.
 36. The agent in accordance with claim24 composed of i) 0.1 to 20% by weight bitumen; ii) 0.01 to 10% byweight of a flux agent, said flux agent being selected from the group ofmembers consisting of multivalent alcohols, bituminous coals, siliconeoils glycols, organopolysiloxanes, any desired mixtures thereof, andpolymethylhydrogensiloxane; iii) 0 to 10% by weight of an additiveselected from the group consisting of cryolite, sodium borate, fluorite,and any desired mixtures of two or more of the above compounds; and iv)a remainder to 100% by weight being calcium oxide or a mixture whichcontains at least 20% by weight of calcium oxide and a remainder to 100%being one or more compounds selected from the group of membersconsisting of calcium hydroxide, calcium carbonate, and any desiredmixtures of the aforesaid compounds.
 37. The agent in accordance withclaim 24, wherein at least the calcium oxide contained in the agent hassuch a distribution of a range of grain sizes that at least 80% byweight of the calcium oxide has a grain size of less than 32 μm.
 38. Theagent in accordance with claim 24 in the form of one or more briquettes,wherein the briquette or briquettes has/have a size (length×width)viewed in cross-section of 10×5 to 200×100 mm.
 39. The agent inaccordance with claim 37 composed of: i) 0.1 to 20% by weight ofbitumen; ii) 0 to 10% by weight of an additive selected from the groupconsisting of cryolite, sodium borate, fluorite, and any desiredmixtures of two or more of the above compounds; and iii) a remainder to100% by weight being calcium oxide or a mixture which contains more than0% by weight of calcium oxide, but at most 99% by weight of calciumoxide and a remainder to 100% being one or more compounds selected fromthe group of members consisting of calcium hydroxide, calcium carbonate,and any desired mixtures of the aforesaid compounds.
 40. A method ofmanufacturing an agent for desulfurizing, the agent comprising calciumoxide, and bitumen; the method comprising the following steps: a) mixingof i) calcium oxide; ii) bitumen; iii) optionally at least one fluxagent; iv) optionally, at least one further additive; as well as v) oneor more calcium compounds selected from the group of members consistingof calcium hydroxide, calcium carbonate, and any desired mixtures of theaforesaid compounds; and b) grinding the mixture obtained in step a) topowder having a distribution of a range of grain sizes in which at least80% by weight of the powder has a grain size of less than 32 μm.
 41. Amethod for slag treatment comprising the step of adding adesulphurization agent to a melt of at least one of a molten pig ironand a molten steel, said agent containing calcium oxide, bitumen as wellas between 0.01 and 10% by weight of at least one flux agent, whereinthe at least one flux agent is selected from the group of membersconsisting of multivalent alcohols, bituminous coal, silicone oils andmixtures thereof, and wherein the agent does not contain any calciumcarbide, any magnesium or any magnesium alloy.
 42. A method inaccordance with claim 41, wherein the agent is introduced into themolten pig iron or into the molten steel by an immersion lance processusing a transport gas or by a stirring-in process.
 43. A method inaccordance with claim 41, wherein the agent is provided in the form ofone or more briquettes and is added into the molten pig iron or into themolten steel for pre-sulfurizing and/or for the slag treatment of moltenpig iron or of molten steel.